Method of making aluminum killed steel



United States Patent o METHOD OF MAKING ALUMINUM STEEL LED William E. Knapp and Wilbur T. Bolkcom, Allison Park,

Pa., assignors to American Metallurgical. Products Company, Pittsburgh, Pa., a partnership of Pennsylvama This invention relates to alloys and methods of making steel and particularly to an addition alloy for imparting cold and hot ductility and for the addition of aluminum to steel with the formation of little or no alumina. The steel industry has for a long time been faced with the problem of alumina segregation in aluminum killed steels. In particular, deep drawing sheet steel, such as is used in automobile body forming has presented recurring problems of alumina inclusion and unsatisfactory cold ductility. In ordinary aluminum killed steels, substantially pure aluminum is added in the ingot mold in the form of pellets or bars. Substantial quantities of alumina are formed by the interaction of the aluminum and oxygen in the molten metal and considerable quantities of this alumina are trapped and held as undesirable alumina segregation.

We have found an alloy by means of which steel may be aluminum killed and yet be free of those undesirable alumina segregations and at the same time have improved hot and cold ductility, particularly expressed in the form of improved impact values, improved reduction of area and elongation and improved plasticity at rolling temperatures The alloy of the present invention has the following broad range of composition:

70% to 96% aluminum 4% to 30% rare earth metals About 80% to 90% aluminum to 20% rare'earch metals The single preferred alloy composition is about 20% rare earth metal and 80% aluminum.

We have found that the alloy is preferably added to the steel in the form of pellets or balls weighing between /2 ounce and 3 ounces, or in notch bars weighing l pound to 5 pounds. Preferably, the alloy is added to the ladle before tapping the steel into the ladle in amounts between about l /2 poundsto 5 pounds per ton of steel, preferably about 2 /2 pounds per ton of steel. We have also found that the alloy may be added to molds. preferably by hanging the alloy in the form of a rod in the central area of the mold and pouring the steel into the mold around the alloy rod.

We have found that the alloy of the present invention and the practice outlined hereinabove makes possible the almost complete elimination of alumina and'alumina in clusions. We have also found that cold ductility is markedly improved so that the steels are more adaptable to difficult forming jobs.

We have found also that there is a greater efficiency in the use of the alloy of the present invention over ordinary aluminum used for killing steel. The efliciency of 2" the present invention is perhaps most clearly set out by the following example:

A bifurcated heat of steel was poured into two ladles of about 170 tons each. In one ladle 850 pounds of conventional 95% aluminum -(810 pounds aluminum) was added. In the other ladle 900 pounds of the alloy of the'present invention'containing 10% rare earth metals and 90% aluminumwas' added '(810 pounds-of aluminum). Analysis showed that the steel in the ladle containing ordinary aluminum obtained an aluminum efliciency of 11.7% and a residual aluminum of 0.026. The steel from the ladle treated with the alloy of the present invention showed a 23% efliciency on the aluminum and an aluminum residual of .05. Comparison of these two steels makes it quite clear that the alloy of the present invention is capable of improving the eificiency of the aluminum additions by about 100% with the residual aluminum increased to about double that which can be expected from conventional aluminum additions.

We have set out hereinabove certain preferred compositions and practices according to our invention. However, it will be understood that the invention may be otherwise embodied within the scope of the following.

claims.v

We claim:

1.. The method of reducing alumina segregation and imparting hot and cold ductility to aluminum killed steel comprising the steps of adding to a ladle an alloy of about 4% to 30% rare earth metals and the balance aluminum with usual impurities in ordinary amounts,

- pouring into the ladle a molten bath of steel to be killed and thereafter teeming the molten product into molds.

2. The method of reducing alumina segregation and imparting hot and cold ductility to aluminum killed steel comprising the steps of adding to a ladle about 1 /2 to Spounds per ton of steel, an alloy of about 4% to 30% rare earth metals and the balance aluminum with usual impurities in ordinary amounts, pouring into the ladle a molten bath of steel to be killed and thereafter teeming the molten product into molds.

3. The method of reducing alumina segregation and imparting hot and cold ductility to aluminum killed steel comprising the steps of adding to a ladle about 3 /2 pounds per ton of steel, an alloy of about 4% to 30% rare earth metals and the balance aluminum with usual impurities in ordinary amounts, pouring into the ladle a moldenbath of steel to be killed and thereafter teeming the molten product into molds.

4. The method of reducing alumina segregation and imparting hot and cold ductility to aluminum killed steels comprising the step of suspending a rod of an alloy of about 10% to 30% rare earth metals and the balance aluminum with usual impurities in ordinary amounts spaced'from the walls of an ingot mold, teeming molten steel about. the rod until the mold is filled and holding the metal in said mold until solidification occurs.

5. The method of reducing alumina segregation'and' imparting hot and cold ductility to aluminum killed steels comprising the steps of. adding about 1% pounds to 5 pounds per ton of an alloy of about 10% to 30% and holding the metal in said mold untilsolidification OCCUIS. v

References Cited in the file of this patent UNITED STATES PATENTS 1,818,556 Iaeger et a1. Aug. 11,1931

I (Other references on following page)- UNITED STATES PATENTS Greenidge Apr. 5, Rohn et a1. Jan. 17, Andrieux Mar. 26, Sarbey Feb. 10, Phelps Oct. 17, Wever et a1. Mar. 29',

FOREIGN PATENTS Great Bfitain Jan. 27, France Mar. 12,

OTHER REFERENCES Rare Metals Handbook, Hampel, 1954, pages 343-344. 7

Aluminum in Iron and Steel, Case and Van Horn, 1953, 5 pages 46-47.

Constitution of Binary Alloys, Hansen, McGraW- Hill Book Company, New York; pages 78-79, 1024-3, 2nd ed., 1958.

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 980529 April 18, 1961 William Ea Knapp et alo that error appears in the above: numbered pat- It is hereby certified ent requiring correction and that the said Letters Patent, should read as "corrected below.

line 4.9 for "earch" read We earth Column 1 for "molden" read m molten column 2 line 47 Signed and sealed this 12th day of September 1961,

(SEAL) Attest:

W. SWID ER v DAVID L. LADD I I Commissioner of Patents Attesting Officer USCOMM-DC- 

1. THE METHOD OF REDUCING ALUMINA SEGREGATION AND IMPARTING HOT AND COLD DUCTILITY TO ALUMINUM KILLED STEEL COMPRISING THE STEPS OF ADDING TO A LADLE AN ALLOY OF ABOUT 4% TO 30% RARE EARTH METALS AND THE BALANCE ALUMINUM WITH USUAL IMPURITIES IN ORDINARY AMOUNTS, POURING INTO THE LADLE A MOLTEN BATH OF STEEL TO BE KILLED AND THEREAFTER TEEMING THE MOLTEN PRODUCT INTO MOLDS. 